A large-size, hard resin roll in the range of 300 mm to 1500 mm in outer diameter, in the range of 1500 mm to 10000 mm in face and of the order in the range of D70 to D99 in hardness (JIS K6253) has been used in various kinds of industries associated with paper making, iron manufacture, fibers, magnetic recording media and the like.
A manufacturing method of a resin roll to which the present invention is directed is basically a method including a procedure in which a synthetic resin outer cylinder molded in the shape of a cylinder is arranged so as to enclose and cover the outer surface of a metal core, a clearance formed between the metal core and the outer cylinder is filled with an adhesive, and the adhesive is hardened to integrate the constituents into one piece through bonding. A manufacturing method of a resin roll according to the procedure is disclosed in detail in Japanese Patent Publication No. 3-47359. Generally, as procedures of a manufacturing method of a resin roll, there have been known in addition to the above-mentioned method: a procedure in which a synthetic resin in a liquid state is cast around a metal core, followed by hardening; a procedure in which a tape-like long strip impregnated with a synthetic resin is wound around the outer surface of a metal core, followed by hardening; and others, to which the present invention does not relate.
The manufacturing process according to Japanese Patent Publication No. 3-47359 is effective especially for manufacturing a large-size, hard resin roll and capable of manufacturing a resin roll, excellent in compressive strength and hard to be damaged on its surface, so that actual achievements thereof have been piled up as a manufacturing method of paper making calender resin roll.
In order to prevent breakage of the outer cylinder during operation, as described in Japanese Patent Publication No. 3-47359, conventionally, it has been accepted that a hardening temperature of the adhesive for bonding the synthetic resin outer cylinder is preferably almost equal to an operating temperature of the resin roll after being manufactured, and an example is specifically shown in the publication thereof that the adhesive is hardened by heating the roll in its entirety in a heating furnace at about 60° C.
A resin roll used in the above described applications is abraded on its surface at proper time for the purpose of removing a damage having generated on the surface of the roll during operation. Abrading water is poured on the roll surface during polishing.
In a resin roll manufactured according to the conventional method, however, a small damage has been easy to be extended to a large crack, when the small damage is present on the roll surface, during polishing, especially under a low temperature condition such as in winter. In addition, there has been a case where a new crack is generated under a low temperature condition. With an enlarged crack thereon, the roll cannot be used any longer. In addition, when a fracture of the roll originating from a crack flies away during polishing, it is considerably dangerous.
It has been considered that in order to provide an adhesive layer of a roll with sufficient strength and durability, the adhesive is effectively hardened at the highest possible temperature to thereby raise a glass transition temperature of the adhesive. However, it has been found that with a rise in a hardening temperature of an adhesive, extension of a crack under a low temperature condition becomes more conspicuous.
It is therefore an object of the present invention to provide a resin roll, having sufficient adhesion strength and durability between a metal core and an outer cylinder and, in addition, suffering no cracking and not extending a damage, if any, to a large crack during polishing a surface of the roll even under a low temperature condition.